I'm trying a very basic PoC, using a VMWare Workstation Windows 10 1709 16299.125 with Test Mode enabled.I didn't sign the drivers at all. I thought the purpose of Test Mode is to test drivers without the need of a signature.

LoadInjectionDriver returns 577

using latest drivers and of-course after using madConfigDrv.exe properly

Disable Secure Boot if it's enabled or download the DSEO (Driver Signature Enforcement Overrider) tool to play with it. You can even perform "Test Signing" if you want to, it does this for you with an NGO signature, nothing else is needed once in Test Mode.